I mocked-up two potential trolley routes. The Mt. Vernon Ave line could happen. In fact, I've even heard rumors that Old Town might want to give up theirs because the in-between businesses miss out on a lot of potential window shoppers. Del Ray and Arlandria don't have the "problem" that Old Town has -- a main attraction. Trolley riders in Old Town are primarily trying to get from the King St. Metro station to the waterfront. In Del Ray and Arlandria, it's more about a sojourn than a destination. The Birchmere could be one destination, but no one is walking from the Braddock Rd. Metro to the Birchmere as it is.
The green colored route would be a nice-to-have whenever Potomac Yard development gets further along and the Potomac Yard Metro gets built (yes, I said when, not if... I'm an optimist).
Take a look, let me know what you think and if you have any other potential stops to add or an idea for a better route.